The invention relates to a method and a device for monitoring the respiration of an individual, especially with a view to detecting a respiratory insufficiency, apnoea or dyspnoea, during the sleep of a baby or of a bedridden patient.
Many cases have been recorded of sudden death of babies or young infants aged from one week to two years due to a dysfunction of the respiratory automatisms. In approximately 75% of these cases of respiratory arrest there are no warning signs.
Early detection of these events thus requires permanent monitoring of the regularity of the respiration of the infants. For this purpose various apparatuses have been proposed, which can be classified in two categories.
A first type of detection apparatus requires a direct contact with the subject. These apparatuses use a displacement transducer which records the variations in the thoracic expansion (extensometer gauge, Hall effect sensor, etc.) or the modification in the distribution of the pressures under the mattress supporting the neonate (capacitive, resistive or inductive effect sensors, or sensors for measuring local pressure). The first are not particularly convenient to use and are the cause of accidents as a result of the permanent connection which there must be between the sleeping infant and the detection apparatus, while the second are expensive, because of the necessary attachment of the network of sensors to the bed of the infant, and are of questionable reliability even when recourse is made to sensors of very great sensitivity.
Since the apparatuses of the second type do not necessitate direct contact with the subject, they have the advantage of not interfering with the movements of the latter during his or her sleep. These apparatuses can be based on the detection of the expiratory breathing (thermistor, infrared photodetector, etc.), but they can then be caused to fail in the event of significant movements of the subject (anterior-posterior or lateral turning). Other apparatuses make use of ultrasonic, infrared or other volumetric sensors: these sensors are well suited when the scene is relatively static, that is to say, when the only movement of the individual is due to his or her breathing, but the information which they supply is more difficult to make use of when the subject moves within the field of observation.
Among the apparatuses for detection without contact there is also known, from French Patent No. 2,141,047; a monitoring apparatus by means of which the body of the individual is subjected to microwave radiation.
As the individual breathes, the frequency of the reflected radiation is different at each instant from that of the incident radiation because of the movement of the wall of the thoracic cage, and the difference in frequency between the waves emitted and the waves received is converted into a signal representing the current rate of movement of the thoracic wall at each instant of the respiratory cycle.
If the level of this signal falls below a certain threshold, and if this situation continues beyond a predetermined period of time, an alarm is triggered, signalling respiratory arrest.
The apparatus therefore comprises a source of microwave radiation which is active, directive and radiates in a very narrow frequency range.
Recourse to the microwave technique requires equipment (aerials, electrical feed circuits and electronic processing circuits) which are relatively expensive and consume large amounts of electrical energy.
The use thereof is tricky and requires certain precautions to be taken so that the results obtained are not falsified by the movements of persons moving around the individual under surveillance, and so that the latter is not subjected to an excessive level of radiated energy. In addition, the consequences of prolonged exposure to microwave radiation are poorly understood, in particular as regards babies.
There is also known, i.e., from U.S. Pat. No. 4,350,166, a method wherein the modulation of the ambient infrared radiations by the carbon dioxide content of the exhalation of an individual is sensed. Thus, the sensors provide modulated signals and, if an interruption in the periodicity of these signal occurs, an alarm is triggered. However, there is always a risk that the ambient atmosphere surrounding the individual is disturbed by extraneous phenomena and that the detection is altered.
The invention aims to provide a method and an apparatus for monitoring the respiration of an individual, which method and apparatus make it possible to overcome the disadvantages of the prior art.
Since the risk factors involved in the respiratory events mentioned above are not known, only monitoring of the infants on a very large scale after their birth would ensure effective prevention. There is thus a need for a means for permitting the respiration of young infants to be monitored both in the hospital environment and at home, for detecting a respiratory insufficiency, apnoea or dyspnoea early, and for triggering an alarm in response to such a detection. Such a means must be adaptable to all sleeping arrangements, not require adjustment, and be easy to use and inexpensive.